The invention relates to a reciprocating piston pump for delivering a liquid, according to the preamble of the independent claim.
EP 1 748 188 A1 shows a reciprocating piston pump for delivering liquid fuel, comprising a solenoid having a coil arranged in a coil carrier. Arranged at an inlet-side end-face opening of the coil carrier is a core flange, which is partially enclosed by the coil carrier. A suction valve seat body, adjoining which is an inlet connection with an inlet port, which is sealed off from the core flange and in which a filter is arranged, is inserted against an internal step of the core flange. A further core part of flange-like design is inserted into the coil carrier at the outlet-side end-face opening of the coil carrier. An actuator, which comprises an armature piston and a piston rod, is axially guided inside the core part in an area still enclosed by the coil, the piston rod being securely connected to the armature piston by a pressed connection. The piston rod is axially guided in a guide bore of a metering cylinder, which is in turn again fixed to an inward-facing step of the flange-like core part. A seat body, which merges into a cylindrical tubular section and into which an outlet port is inserted and sealed off, is inserted from the side opposite the piston rod, the tubular section being screwed into an end thread of the core part. A valve spring biasing a closing element in the form of a ball towards a tapered valve seat is braced against an end face of the outlet port inserted into the tubular section, wherein the valve seat and the closing element define a linear contact. An impact damper, which is intended to damp the stroke movements of the piston rod, is inserted into the guide bore on the side of the guide bore facing the valve seat. The metering cylinder has two radial bores, which ensure a fluid connection between the guide bore of the metering cylinder and a pump chamber located outside the metering cylinder and enclosed by the flange-like core part. With no current passing through the coil, the armature piston is prestressed towards the outlet port by a helical coil spring, which is braced against the suction valve seat body. When a current passes through the coil, the armature piston is shifted towards the inlet port, wherein the return stroke ensued under the prestressing of the helical coil spring expells the liquid from the delivery chamber. An end-face impact damper is also provided at the end face of the armature piston remote from the piston rod, in order to damp impacts against the suction valve seat body. A draw back of the known reciprocating piston pump are the many parts and the numerous sealing points required, which are continuously shaken by the pump movements and therefore have a tendency to leak, especially as the pump warms up, leading to different rates of thermal expansion of the various materials. Inserting the impact dampers into the guide bore is intricate, as is pressing the metering cylinder into the core part, which is held only at the end and thereby has a tendency to jam. The canister-shaped armature piston needs to have a comparatively large distance between it and the core part guiding it, in order to create a gap for passage of the liquid, whereby the magnetic power suffers and impaired liquid flow conditions ensue. The pump is designed for a specific swept volume and must be modified as a whole if a different volume is to be delivered. The delivery capacity is limited by the liquid gap, which is provided between the armature piston and the core flange and which restricts the passage of the liquid. At the same time the liquid gap in relation to the armature adversely affects the utilization of the field generated by the coil.
DE 103 60 706 A1 shows a solenoid-actuated check valve, comprising a closing element in the form of a ball and a valve seat formed in a seat body. The seat body is enclosed by an annular solenoid, which encloses the valve seat and part of the closing element, and when energized magnetically draws the closing element into the valve seat. The valve seat is embodied as a spherical segment having a radius of curvature corresponding to the radius of curvature of the closing element. An annular recess, which is filled by an elastomer seal, is provided in the valve seat, wherein the elastomer seal causes sealing with the closing element. A further annular elastomer area is provided in an extension of the valve seat, and comes into contact with the closing element when the solenoid is actuated. One disadvantage is the additional electrical supply required for actuation of the check valve. The known valve is furthermore not suited to installation in a solenoid-actuated pump, since the magnetic fields would interfere with one another.